d.c. Magnetic fields of the human leg as a function of position and relaxation

Grimes, D. I. F.; Lennard, R.; Swithenby, S. J.

doi:10.1007/bf02455962

Cited by 12 publications

(6 citation statements)

References 5 publications

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“…The electrical detection of these types of injury currents is complicated by the difficulties associated with obtaining high-quality direct-coupled electrode recordings, especially because of the potentially large and fluctuating junction potentials at the electrode-tissue interface. Magnetic recording of these electrical activities overcomes many of these difficulties, and for this reason, injury currents in the brain and heart have been studied magnetically (2,18,(25)(26)(27) as well as injury currents from peripheral nerves and muscles (28)(29)(30)(31)(32)(33)40).…”

Section: Discussionmentioning

confidence: 99%

“…SQUID magnetometers have been utilized to measure the injury currents associated with spreading depression due to migraine in humans, in acute myocardial ischemia in rabbit hearts, and in humans with left bundle branch block (2,(25)(26)(27). In addition to these applications, SQUIDs are able to measure injury currents in peripheral nerve and muscle (28)(29)(30)(31)(32)(33) and also from bean plants (34). To date, no measurements of the DC injury currents associated with ischemia of the gastrointestinal tract have been reported, but the syncytial nature of intestinal smooth muscle suggests that these currents should be present.…”

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confidence: 99%

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Biomagnetic Detection of Injury Currents in Rabbit Ischemic Intestine

et al. 2005

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The presence of direct current (DC) injury currents in ischemic tissue is an important diagnostic indicator of pathophysiology in cortical spreading depression and particularly in myocardial infarction. To date, no measurements of DC injury currents in the alimentary tract have been reported. We used a SQUID magnetometer to measure changes in the baseline of the magnetic field of intestinal electrical activity during induced segmental ischemia. We computed the magnetic field DC baseline by subtracting sequential recordings made while the bowel segment was first directly beneath the SQUID and then pulled away. We observed a significant baseline decrease of 38% ± 4% in experimental animals, while the control group decreased by only 1% ± 6%. This magnetic field baseline decrease is consistent with the flow of injury currents between normally perfused and hypoxic tissue regions. This study is the first report of DC injury currents in ischemic smooth muscle of the alimentary tract. KEY WORDS: magnetogastrogram; magnetoenterogram; electrogastrogram; intestinal ischemia.Despite the high morbidity and mortality associated with intestinal ischemia and the relatively large body of literature detailing the underlying causative mechanisms, a reliably sensitive and specific diagnostic technique remains elusive (1). Previous studies from our and other laboratories have shown that intestinal ischemia alters the slow wave of the intestine in the early stages of ischemia, suggesting the potential utility of noninvasive methods that detect intestinal slow wave (2). Ischemia decreases both the frequency and the amplitude of the slow wave (3), and in certain cases, tachyarrhythmias are observed (4). We have previously shown that superconducting quantum interference device (SQUID) magnetometers are able to Manuscript

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Biomagnetic Detection of Injury Currents in Rabbit Ischemic Intestine

et al. 2005

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“…Furthermore, SQUIDs have been utilized to detect injury currents in peripheral nerve and muscle and in bean plants [8,[10][11][12]15]. Our research group has already measured injury currents in ischemic intestinal smooth muscle using a SQUID magnetometer [2,21,23].…”

Section: Introductionmentioning

confidence: 99%

Biomagnetic Investigation of Injury Currents in Rabbit Intestinal Smooth Muscle During Mesenteric Ischemia and Reperfusion

et al. 2006

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A noninvasive, sensitive, and specific method of detecting mesenteric ischemia would be of great use in reducing the morbidity and mortality with which it is associated. Acute lesions in polarized electrically coupled tissues lead to injury currents driven by the transmembrane resting potential gradient. These injury currents are an effective indicator of pathophysiology. The presence of near-DC injury currents in rabbit intestinal smooth muscle has already been demonstrated using a Superconducting quantum interference device (SQUID), and the aim of this study was to evaluate the effect of arterial reperfusion upon these currents. We exteriorized the small bowel of 14 New Zealand white rabbits and placed a remotely operated vascular occluder around the distal most artery supplying a 3-in segment of the jejunum. Experiments were conducted in three groups, i.e., control (n=3), ischemia (n=6), and reperfusion following ischemia (n=5). The subject's position was modulated in and out of the biological field detection range of a SQUID magnetometer using a lift constructed of nonmagnetic material. The changes in magnetic field amplitude were 9.3 and 31.01% for the control and ischemia groups, respectively. The reperfusion group first exhibited a decrease of 17.35% from the pre-ischemic to the ischemic period, followed by an increase of 13.88% of the ischemic value after reestablishing perfusion. In conclusion, injury currents in GI smooth muscle that appear during ischemia are reduced to near-pre-ischemic levels during reperfusion.

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“…Despite the apparent motivations for magneto-physiological measurements, the very small signal size (<10 pT) has limited widespread adoption of biomagnetic measurements as a routine clinical measurement, since this regime of sensitivity has been limited to SQUIDs 20 (superconducting quantum interference devices), which require liquid helium cooling. As a result, while SQUIDs have been for decades used for detection of biomagnetic signals 15,[21][22][23] , the associated measurement systems are bulky, expensive, and ill-suited to the different geometries of various body parts, limiting these systems practical utility. Recent developments in atomic magnetometry have led to new, highsensitivity devices known as optically pumped magnetometers (OPMs) 24 that are uncooled, centimeter-scale, and relatively low cost -characteristics necessary to make magneto-physiological measurements an accessible diagnostic tool.…”

Section: Introductionmentioning

confidence: 99%

Biomagnetic signals recorded during transcranial magnetic stimulation (TMS)-evoked peripheral muscular activity

Iwata¹,

Hu²,

Sander³

et al. 2019

Preprint

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Transcranial magnetic stimulation (TMS) has widespread clinical applications from diagnosis to treatment approaches. We combined TMS with non-contact magnetic detection of TMS-evoked muscle activity in peripheral limbs to explore a new diagnostic modality that enhances the utility of TMS as a clinical tool by leveraging technological advances in magnetometry. We recorded measurements inside of a hospital using an array of optically pumped magnetometers (OPMs) inside a portable shield that encompasses only the forearm and hand of the subject. We present magnetomyograms (MMG)s of TMS-evoked movement in a human hand, together with a simultaneous surface electromyograph (EMG) and electroencephalograph (EEG) data. The biomagnetic signals recorded in the MMG provides detailed spatial and temporal information that is complementary to that of the electric signal channels. Moreover, we identify features in the magnetic recording beyond that of the EMG, at time points which we further analyze in the EEG. This system demonstrates the value of biomagnetic signals in TMS-based clinical approaches and widens its availability and practical potential.

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d.c. Magnetic fields of the human leg as a function of position and relaxation

Cited by 12 publications

References 5 publications

Biomagnetic Detection of Injury Currents in Rabbit Ischemic Intestine

Biomagnetic Detection of Injury Currents in Rabbit Ischemic Intestine

Biomagnetic Investigation of Injury Currents in Rabbit Intestinal Smooth Muscle During Mesenteric Ischemia and Reperfusion

Biomagnetic signals recorded during transcranial magnetic stimulation (TMS)-evoked peripheral muscular activity

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